How write a Django REST APIView POST request with a condition? - api

Question

I am trying to create a post request for a game api. The game implies that a user can label a picture. A label entered once is a tagging, a label entered twice for the same resource is a tag.
This is how I am trying to create a Tagging so far:
saved_tagging = Tagging.objects.create(user_id=current_user_id,
gameround=gameround,
resource=random_resource,
tag='tag newwww',
created=datetime.now(),
score=score,
origin=origin
)
tagging_serializer = TaggingSerializer(saved_tagging)
At the moment I am getting the ValueError: Cannot assign "'tag newwww'": "Tagging.tag" must be a "Tag" instance.
Is there any way that I can avoid this?
Here are also my models and the relevant serializer.
models.py
class Tag(models.Model):
name = models.CharField(max_length=256)
language = models.CharField(max_length=256)
objects = models.Manager()
def create(self, validated_data):
tag_data = validated_data.pop('tag')
Tag.objects.create(**tag_data)
return tag_data
def __str__(self):
return self.name or ''
class Tagging(models.Model):
user = models.ForeignKey(CustomUser, on_delete=models.SET_NULL, null=True)
gameround = models.ForeignKey(Gameround, on_delete=models.CASCADE, related_name='taggings')
resource = models.ForeignKey(Resource, on_delete=models.CASCADE, related_name='taggings')
tag = models.ForeignKey(Tag, on_delete=models.CASCADE, related_name='tagging')
created = models.DateTimeField(editable=False)
score = models.PositiveIntegerField(default=0)
origin = models.URLField(max_length=256, blank=True, default='')
objects = models.Manager()
def create(self, validated_data):
tag_data = validated_data.pop('tag')
tagging = Tagging.objects.create(**validated_data)
Tag.objects.create(name=tagging, **tag_data)
return tagging
def __str__(self):
return str(self.tag) or ''
serializers.py
class TaggingSerializer(serializers.ModelSerializer):
tag = StringRelatedField()
resource = ResourceSerializer(read_only=True)
gameround = GameroundSerializer(read_only=True)
class Meta:
model = Tagging
fields = ('id', 'tag', 'gameround', 'created', 'score', 'resource', 'origin')
def create(self, validated_data):
return Tagging.objects.create(**validated_data)
def to_representation(self, data):
data = super().to_representation(data)
return data

Answer 1

tag must be a Tag Instance !
So... you can do this in two ways (in my opinion).
First you can create a Tag object in your view and than pass this object to tag value in your Tagging create method.
Or create a service layer on your app, and create a custom create method for your model. This in my opinion is superior because your a centralizing your rules in one method instead of in one view.
Ex.:
services/tag_service.py
def create(user_id,gameround,resource,tag,...origin):
if not isinstance(tag, Tag):
#create your tag model based on the String passed
your_new_tag_object = Tag.objects.create(tag=tag, ...)
# Here your create others rules too for model creation
# Return your model .create method
return Tagging.objects.create(user_id=user_id,...tag=your_new_tag_object,...)
And Than use this new create method inside your POST serializer.
from services import tag_service
class TaggingSerializer(serializers.ModelSerializer):
# your normal serializer here
def create(self, validated_data):
return tag_service.create(**validated_data)